If this has been posted, my search didn't uncover it.  It is
pretty interesting--ex-VW engineer, boxer engine.  Our Vanagons
should last long enough to get one of these.

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This is no wimp engine.
It's a two cylinder with four pistons
delivering 300+ Horse Power
It's extremely small and very efficient and
is presently in use in test applications
The configuration below is equivalent to a
extremely ballsy four cylinder engine
When doubled, it's an extremely ballsy 600+
H.P. engine

It's called OPOC (Opposed Piston Opposed
Cylinder), and it's a turbocharged two-stroke, two-cylinder, with four
pistons, two in each cylinder, that will run on gasoline, diesel or ethanol.
The two pistons, inside a single cylinder, pump toward and away from each
other, thus allowing a cycle to be completed twice as quickly as a
conventional engine while balancing its own loads.

The heavy lifting for this unconventional
concept was performed Prof. Peter Hofbauer. During his 20 years at VW,
Hofbauer headed up, among other things, development of VW's first diesel
engine and the VR6.
The OPOC has been in development for several
years, and the company claims it's 30 percent lighter, one quarter the size
and achieves 50 percent better fuel economy than a conventional turbo
diesel engine.

They're predicting 100 MPG in a conventional car.

http://www.engineeringtv.com/video/Opposed-Piston-Opposed-Cylinder
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